remove non free books and broken links (#448)

README.md

@@ -804,12 +804,7 @@ Various resources, such as books, websites and articles, for improving your skil
 
 *Sysadmin related books.*
 
-- [Codex](http://www.starkandwayne.com/codex/) - How to deploy Cloud Foundry PaaS on infrastructures like AWS, OpenStack, Azure by Stark & Wayne, LLC.
 - [The Linux Command Line](http://linuxcommand.org/tlcl.php) - A book about the Linux command line by William Shotts.
-- [The Phoenix Project: A Novel about IT, DevOps, and Helping Your Business Win](http://itrevolution.com/books/phoenix-project-devops-book/) - How DevOps techniques can fix the problems that happen in IT organizations.
-- [The Practice of System and Network Administration](http://everythingsysadmin.com/books.html) - The first and second editions describes the best practices of system and network administration, independent of specific platforms or technologies.
-- [The Visible Ops Handbook: Implementing ITIL in 4 Practical and Auditable Steps](http://www.itpi.org/the-visible-ops-handbook-review.html) - Is a methodology designed to jumpstart implementation of controls and process improvement.
-* UNIX and Linux System Administration Handbook (ISBN-13: 978-0131480056) - Approaches system administration from a practical perspective.
 
 
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